diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/context/RootContext.java b/compiler/backend/src/org/jetbrains/jet/codegen/context/RootContext.java
index c8393d4f086..97d6bd62649 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/context/RootContext.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/context/RootContext.java
@@ -54,7 +54,7 @@ class RootContext extends CodegenContext {
         }
 
         @Override
-        public DeclarationDescriptor substitute(TypeSubstitutor substitutor) {
+        public DeclarationDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
             throw new IllegalStateException();
         }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractNamespaceDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractNamespaceDescriptorImpl.java
index be747d528a4..4d432454fd9 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractNamespaceDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractNamespaceDescriptorImpl.java
@@ -51,7 +51,7 @@ public abstract class AbstractNamespaceDescriptorImpl extends DeclarationDescrip
 
     @NotNull
     @Override
-    public NamespaceDescriptor substitute(TypeSubstitutor substitutor) {
+    public NamespaceDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException("This operation does not make sense for a namespace");
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractReceiverParameterDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractReceiverParameterDescriptor.java
index 8000bf7e8bc..bdebad9f39d 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractReceiverParameterDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/AbstractReceiverParameterDescriptor.java
@@ -16,6 +16,7 @@
 
 package org.jetbrains.jet.lang.descriptors;
 
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.lang.descriptors.annotations.AnnotationDescriptor;
 import org.jetbrains.jet.lang.resolve.name.Name;
@@ -35,7 +36,7 @@ public abstract class AbstractReceiverParameterDescriptor extends DeclarationDes
 
     @Nullable
     @Override
-    public ReceiverParameterDescriptor substitute(TypeSubstitutor substitutor) {
+    public ReceiverParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         if (substitutor.isEmpty()) return this;
         JetType substitutedType = substitutor.substitute(getType(), Variance.INVARIANT);
         if (substitutedType == null) return null;
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/CallableDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/CallableDescriptor.java
index 5f1fb17f3be..fc6467321f8 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/CallableDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/CallableDescriptor.java
@@ -45,7 +45,7 @@ public interface CallableDescriptor extends DeclarationDescriptorWithVisibility,
     CallableDescriptor getOriginal();
 
     @Override
-    CallableDescriptor substitute(TypeSubstitutor substitutor);
+    CallableDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     @NotNull
     List<ValueParameterDescriptor> getValueParameters();
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
index c9934bf8b20..5c55817c3e3 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptor.java
@@ -50,7 +50,7 @@ public interface ClassDescriptor extends ClassifierDescriptor, MemberDescriptor,
 
     @NotNull
     @Override
-    ClassDescriptor substitute(TypeSubstitutor substitutor);
+    ClassDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     @Nullable
     @Override
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorBase.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorBase.java
index 3e529a8dd10..1e541c6353a 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorBase.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorBase.java
@@ -50,7 +50,7 @@ public abstract class ClassDescriptorBase implements ClassDescriptor {
 
     @NotNull
     @Override
-    public ClassDescriptor substitute(TypeSubstitutor substitutor) {
+    public ClassDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         if (substitutor.isEmpty()) {
             return this;
         }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorImpl.java
index 0bcd62ac68e..cbf6aba7ea7 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ClassDescriptorImpl.java
@@ -120,7 +120,7 @@ public class ClassDescriptorImpl extends DeclarationDescriptorNonRootImpl implem
 
     @NotNull
     @Override
-    public ClassDescriptor substitute(TypeSubstitutor substitutor) {
+    public ClassDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException(); // TODO
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/DeclarationDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/DeclarationDescriptor.java
index 469fabd0e6a..55572df16b2 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/DeclarationDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/DeclarationDescriptor.java
@@ -35,7 +35,7 @@ public interface DeclarationDescriptor extends Annotated, Named {
     DeclarationDescriptor getContainingDeclaration();
 
     @Nullable
-    DeclarationDescriptor substitute(TypeSubstitutor substitutor);
+    DeclarationDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     <R, D> R accept(DeclarationDescriptorVisitor<R, D> visitor, D data);
     void acceptVoid(DeclarationDescriptorVisitor<Void, Void> visitor);
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptor.java
index a04b732f744..4a7d44d653c 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptor.java
@@ -31,7 +31,7 @@ public interface FunctionDescriptor extends CallableMemberDescriptor {
     FunctionDescriptor getOriginal();
 
     @Override
-    FunctionDescriptor substitute(TypeSubstitutor substitutor);
+    FunctionDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     @Override
     @NotNull
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptorImpl.java
index f71b3f0b529..9154e0c3055 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/FunctionDescriptorImpl.java
@@ -178,7 +178,7 @@ public abstract class FunctionDescriptorImpl extends DeclarationDescriptorNonRoo
     }
 
     @Override
-    public final FunctionDescriptor substitute(TypeSubstitutor originalSubstitutor) {
+    public final FunctionDescriptor substitute(@NotNull TypeSubstitutor originalSubstitutor) {
         if (originalSubstitutor.isEmpty()) {
             return this;
         }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LazySubstitutingClassDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LazySubstitutingClassDescriptor.java
index 8c0058c9f9b..c209fdc9a30 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LazySubstitutingClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LazySubstitutingClassDescriptor.java
@@ -141,7 +141,7 @@ public class LazySubstitutingClassDescriptor implements ClassDescriptor {
 
     @NotNull
     @Override
-    public ClassDescriptor substitute(TypeSubstitutor substitutor) {
+    public ClassDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         if (substitutor.isEmpty()) return this;
         return new LazySubstitutingClassDescriptor(this, TypeSubstitutor.create(substitutor.getSubstitution(), getSubstitutor().getSubstitution()));
     }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LocalVariableDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LocalVariableDescriptor.java
index 063d4956065..7ba99d7cba2 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LocalVariableDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/LocalVariableDescriptor.java
@@ -41,7 +41,7 @@ public class LocalVariableDescriptor extends VariableDescriptorImpl {
 
     @NotNull
     @Override
-    public LocalVariableDescriptor substitute(TypeSubstitutor substitutor) {
+    public LocalVariableDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException(); // TODO
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ModuleDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ModuleDescriptor.java
index 2f8c6ea104e..9da1e43c579 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ModuleDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ModuleDescriptor.java
@@ -57,7 +57,7 @@ public class ModuleDescriptor extends DeclarationDescriptorImpl implements Class
 
     @NotNull
     @Override
-    public ModuleDescriptor substitute(TypeSubstitutor substitutor) {
+    public ModuleDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         return this;
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyAccessorDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyAccessorDescriptor.java
index 2afaf3b12dd..e01c9c31721 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyAccessorDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyAccessorDescriptor.java
@@ -73,7 +73,7 @@ public abstract class PropertyAccessorDescriptor extends DeclarationDescriptorNo
 
     @NotNull
     @Override
-    public FunctionDescriptor substitute(TypeSubstitutor substitutor) {
+    public FunctionDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException(); // TODO
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptor.java
index 4c05ca5fe7c..6984306b448 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptor.java
@@ -44,5 +44,5 @@ public interface PropertyDescriptor
     Set<? extends PropertyDescriptor> getOverriddenDescriptors();
 
     @Override
-    PropertyDescriptor substitute(TypeSubstitutor substitutor);
+    PropertyDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptorImpl.java
index 4b1b27b7177..08262972433 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/PropertyDescriptorImpl.java
@@ -195,7 +195,7 @@ public class PropertyDescriptorImpl extends VariableDescriptorImpl implements Pr
     }
 
     @Override
-    public PropertyDescriptor substitute(TypeSubstitutor originalSubstitutor) {
+    public PropertyDescriptor substitute(@NotNull TypeSubstitutor originalSubstitutor) {
         if (originalSubstitutor.isEmpty()) {
             return this;
         }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ReceiverParameterDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ReceiverParameterDescriptor.java
index 35d1b14e75c..7655de701e4 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ReceiverParameterDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ReceiverParameterDescriptor.java
@@ -40,5 +40,5 @@ public interface ReceiverParameterDescriptor extends DeclarationDescriptor {
 
     @Nullable
     @Override
-    ReceiverParameterDescriptor substitute(TypeSubstitutor substitutor);
+    ReceiverParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ScriptDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ScriptDescriptor.java
index 78c6d5ab05e..16775bb2f92 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ScriptDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ScriptDescriptor.java
@@ -157,7 +157,7 @@ public class ScriptDescriptor extends DeclarationDescriptorNonRootImpl {
     }
 
     @Override
-    public DeclarationDescriptor substitute(TypeSubstitutor substitutor) {
+    public DeclarationDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new IllegalStateException("nothing to substitute in script");
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptor.java
index bcabda7a2e1..6a2f7f622b1 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptor.java
@@ -48,7 +48,7 @@ public interface TypeParameterDescriptor extends ClassifierDescriptor {
     @NotNull
     @Override
     @Deprecated // Use the static method TypeParameterDescriptor.substitute()
-    TypeParameterDescriptor substitute(TypeSubstitutor substitutor);
+    TypeParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     int getIndex();
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptorImpl.java
index a51ad9e607a..5a5a8fa2878 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/TypeParameterDescriptorImpl.java
@@ -198,7 +198,7 @@ public class TypeParameterDescriptorImpl extends DeclarationDescriptorNonRootImp
     @NotNull
     @Override
     @Deprecated
-    public TypeParameterDescriptor substitute(TypeSubstitutor substitutor) {
+    public TypeParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException();
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ValueParameterDescriptorImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ValueParameterDescriptorImpl.java
index 072aa7ff730..769a97fb725 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ValueParameterDescriptorImpl.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/ValueParameterDescriptorImpl.java
@@ -126,7 +126,7 @@ public class ValueParameterDescriptorImpl extends VariableDescriptorImpl impleme
 
     @NotNull
     @Override
-    public ValueParameterDescriptor substitute(TypeSubstitutor substitutor) {
+    public ValueParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException(); // TODO
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/VariableDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/VariableDescriptor.java
index c355a2641b7..ef8783889f3 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/VariableDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/descriptors/VariableDescriptor.java
@@ -30,7 +30,7 @@ public interface VariableDescriptor extends CallableDescriptor {
     DeclarationDescriptor getContainingDeclaration();
 
     @Override
-    VariableDescriptor substitute(TypeSubstitutor substitutor);
+    VariableDescriptor substitute(@NotNull TypeSubstitutor substitutor);
 
     boolean isVar();
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyTypeParameterDescriptor.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyTypeParameterDescriptor.java
index c9bf07c6b6a..d7bdaa9ad11 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyTypeParameterDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyTypeParameterDescriptor.java
@@ -241,7 +241,7 @@ public class LazyTypeParameterDescriptor implements TypeParameterDescriptor, Laz
     @NotNull
     @Override
     @Deprecated
-    public TypeParameterDescriptor substitute(TypeSubstitutor substitutor) {
+    public TypeParameterDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
         throw new UnsupportedOperationException("Don't call substitute() on type parameters");
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/types/ErrorUtils.java b/compiler/frontend/src/org/jetbrains/jet/lang/types/ErrorUtils.java
index d16d08ebd5a..7df56f6e550 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/types/ErrorUtils.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/types/ErrorUtils.java
@@ -130,7 +130,7 @@ public class ErrorUtils {
 
         @NotNull
         @Override
-        public ClassDescriptor substitute(TypeSubstitutor substitutor) {
+        public ClassDescriptor substitute(@NotNull TypeSubstitutor substitutor) {
             return ERROR_CLASS;
         }
     };